Many people jumped into the river from the London Duck Tours craft.
All the passengers and crew were rescued by the emergency services and a passing tourist boat yesterday.
Those rescued were mainly "wet and cold", said London Ambulance. Some people had suffered the effects of inhaling smoke.
Three people were taken to hospital "as a precaution" said an ambulance service spokeswoman.
Those on board are believed to have included visitors from the UK, Brazil, Russia, Australia and Sweden, the BBC reported.
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One of the passengers, Donna Wood said she jumped from the craft.
"I was scared the boat might blow. It was scary. There was a lot of smoke inhalation, so we jumped in the water."
London Fire Brigade station manager Simon Tuhill the 30 people on the boat ended up in the water.
"A number of people were recovered from the water. All 28 passengers and two crew members have been accounted for," a Scotland Yard spokesman said.
The fire service has begun an investigation into how the fire started.
In a statement, managing director of the company John Bigos said: "The company acknowledges the distressing situation experienced by our passengers.
"However, we are pleased to report that all persons involved in the incident are safe and well.
"Until the cause is established, the company will not be operating on the river....," Bigos said.